This is not an official news source for CineForm or GoPro product releases, just some bits and pieces of stuff I happen to be working on. My work and hobbies are pretty much the same thing. -- David Newman

Monday, July 02, 2007

While this post is aimed squarely at those doing films in the San Diego division of the 48 hour Film Project (yes, many of my posts will be on this topic for a while), I hope this information is general enough for anyone producing a short/feature for HD presentation.

As CineForm will be re-mastering all 50 films for their theatrical presentation starting two days later, we had to determine the best way to handle the range of input formats without degrading the overall presentation quality. Years of seeing my own HD work crushed to letterboxed SD drove this years CineForm involvement. While projecting HD as HD and SD and SD is simple enough, we found in our theater tests that the projector format-switching introduces unwanted garbage on the screen as the projector re-syncs -- one of the projectors even required realigning the display after each format switch (although not the Sony 4k.) With common format ranging form SD 60i, SD 24p, 720p, 1080i60 and 1080p24, we were in for a lot of projector switching. For this reason, we are re-mastering all submissions to 1920x1080 and projecting at 24 frames per second, i.e. more work for CineForm.

As 24p is not perfect, it is a good idea for filmmakers to consider its minor limitations. It is best to avoid excessive camera motion, particularly if you are shooting 60i SD or HDV, which is more forgiving of camera movement. In most situations, cameras on tripods or with slow camera movements typically translate better to the big screen. Also, as the presentation is 16x9 wide-screen, use it if your camera supports this mode. If you are using letterbox on a 4x3 camera, we will scale the active picture to fill the screen. Full screen 4x3 shorts will be kept in their original format; the source aspect ratio will be preserved for all content.

Clearly, 24p sources work the best; however, converting 60i to 24p is not too difficult to achieve nice results. However, 30p or "frame mode" common on many cameras should be avoided, as that doesn't convert to 24p well.

Most of the above advice is pretty straight forward and standard, but then I considered the number for very nice 24p sources (like Sony's V1U and Canon's HV20) that are not supported within popular NLEs (e.g. Apple FCP.) 24p editing on a 60i timeline is far more common than it should be, and just like interlace video, it should be outlawed. :) The issue is that each 24p clip on a 60i timeline will not have the same "cadence;" with each cut potentially making sequences with half frame lengths, making a good 24p master is nearly impossible, and that is not even considering what happens with dissolves. Clearly, if you can edit 24p on a 24p timeline, do it! Fortunately, CineForm customers don't have this issue, but I couldn't recommend that all filmmakers learn new software for this project. So at first I though we couldn't support bad cadence 24p (in 60i), particularly with a very short time-frame to remaster so many films, but then I saw it as an opportunity to upgrade our internal 60i to 24p algorithms to handle this craziness. That is what I've been working on this weekend, and the San Diego audience will see it in action in two weeks and see that it works pretty well.

12 comments:

So CineForm can now do reverse 3:2 pulldown cadence detection per-shot? That would actually be very nice, as that is the bane of having a 60i master from a 24P source . . . I believe some encoding products like Squeeze or ProCoder can do this type of detection, but I could see a number of uses for it inside of HD-Link since Squeeze or Procoder don't support the higher-end bit-depth formats

"CineForm can now do reverse 3:2 pulldown cadence detection per-shot?"

Yes, that is basically it. One thing we do a little differently, is this will work live while capturing from a poorly constructed tape. There are likely some decisions that you have to do on the fly that you wouldn't do for a render of conversion, but this was designed for speed.

As HDV is MPEG2 it is best not to export back to that heavily compressed format -- for quality and export speed reasons. We can accept an HDV tape very easily, however you should consider exporting your timeline to an intermediate format like Apple ProRes 422 or CineForm Intermediate are good choices, DVCPRO-HD if that is all you have. If you have edited using 60i timeline if you NLE doesn't support 24p editing of HDV (most don't), make sure you export to a 60i file. We can accept this data on a DVD data disk or even a FireWire drive (saving you the burn time.)

Convert 60i which is 1440x540 fields at 60Hz, will never resolve to 1080p24/30, there is always some vertical loss to any deinterlacer. That is way we have 24p cameras. The CineForm detinterlacer does use top and bottom fields to construct a frame a vertical resolution is pretty good.